Note on line chart
This section is tightly linked with other sections. A connected scatterplot is almost the same thing, but each observation is represented as a dot. An area chart fills the surface between the line and the X axis. More generally, the time series section can interest you.
connected scatter area chart time series
Step by step with ggplot2
ggplot2 allows to draw line charts thanks to the geom_line() function. It expects as input a data frame with 2 numeric variables, one displayed on each axis. Start your journey with the most basic line chart.
Most basic Most basic line chart with R and ggplot2
Basic customization Basic customization to improve the line chart: size, color, type, theme, title and more
Log transform How to use a log transformation for the Y axis with scale_x_log10().
Deal with date How to avoid struggling with dates on the X axis
Basic Grouped line chart How to build a line chart representing several groups
Customized Grouped Pick up a nice color palette, use a theme, add titles, and more.
Linear trend geom_smooth allows to add the result of a model to your scatterplot, with confidence interval as well.
Annotation Annotation allows to highlight main features of a chart. Learn how to add text, circles, lines and more.
Dual Y axis A few examples showing how to use the sec.axis argument to add a second Y axis.
geom_ribbon and geom_smooth
Line charts are often displayed together with confidence intervals. ggplot2 offers 2 main functions to build them. geom_ribbon allows to build the area around the curve from precomputed values. geom_smooth will compute a model for you and plot the result directly.
Geom_smooth() geom_smooth allows to add the result of a model to your scatterplot, with confidence interval as well.
Geom_ribbon() If you already know the upper and lower limits of the error envelop, geom_ribbon will plot it for you.
Mind the Spaghetti (ggplot2)
When too many groups are displayed on the same line chart it gets very hard to get insight from the figure. This is commonly called a spaghetti chart. Here are a few alternatives using ggplot2: annotation and small multiple.
Step by step with base R
In base R, the line function allows to build quality line charts.
Line color and Y value Change the line color according to the Y axis value
How to add a legend to base R plot The legend() function allows to add a legend. See how to use it with a list of available customization.
Reversed Y axis Learn how to flip the Y axis upside down using the ylim argument.
Polynomial curve Line charts are often used to represent the result of a statistical model.
Parameters reminder A cheatsheet to quickly reminder what option to use with what value to customize your chart.
Dual Y axis with ggplot2
Warning: a dual Y axis line chart represents the evolution of 2 series, each plotted according to its own Y scale. This kind of chart must be avoided, since playing with Y axis limits can lead to completely different conclusions. Visit data-to-viz for more info.
Why you should avoid it
Most basic dual Axis Most basic usage of sec.axis attribute to display a second Y axis.
More style Customize the chart style with title, colors, theme and more.
Mix geoms A dual axis chart mixing a line chart with a barplot.
Dual Y axis with latticeExtra
Warning: a dual Y axis line chart represents the evolution of 2 series, each plotted according to its own Y scale. This kind of chart must be avoided, since playing with Y axis limits can lead to completely different conclusions. Visit data-to-viz for more info.
Why you should avoid it
Line chart with 2 series A classic line chart with 2 series, only 1 Y axis.
Dual Y axis line chart Add a second Y axis for the second sery. See how chart conclusion gets different and wrong.
Add legend Add a legend to specify what color is linked to what value.
